1. Field of the Invention
The present invention relates generally to power over Ethernet (PoE) and, more particularly, to a PoE powered device with power fallback states.
2. Introduction
In a PoE application such as that described in the IEEE 802.3af and 802.3at specifications, a power sourcing equipment (PSE) can deliver power to a powered device (PD) over Ethernet cabling. Various types of PDs exist, including voice over IP (VoIP) phones, wireless LAN access points, Bluetooth access points, network cameras, computing devices, etc.
In accordance with IEEE 802.3af, a PSE can deliver up to 15.4 W of power to a single PD over two wire pairs. In accordance with IEEE 802.at, on the other hand, a PSE may be able to deliver up to 30 W of power to a single PD over two wire pairs. Other proprietary solutions can potentially deliver higher or different levels of power to a PD. A PSE may also be configured to deliver power to a PD using four wire pairs.
In one application, PoE can be used to provide power backup for a device. In other words, the device can be designed to receive power primarily from a local power source such as a power-supply brick plugged into a wall outlet or power strip. Only in the event of a failure in the local power source would the device need to be supplied with power from the backup PoE power source.
In this power backup application, it is important that the transition between the primary local power source and the backup PoE power source occurs seamlessly. As would be appreciated, a seamless transition between the primary local power source and the backup PoE power sources would ensure that the device operates predictably during the transition. What is needed therefore is a mechanism that enables a PD to manage effectively the loss of a local power supply.